This is an observational study which hopes to answer the question of whether the amount of coughing that occurs when a patient emerges from anaesthesia has a negative impact on the ability of the lung to transfer oxygen to the blood in the post anaesthetic care unit (PACU). The patients' involvement starts 45 minutes before the anticipated end of surgery when a standard lung recruitment manoevre will be performed. Fifteen minutes later a 2ml blood sample is taken from the arterial catheter which was placed at the beginning of surgery. From this, together with routinely monitored clinical data, the alveolar/arterial oxygen difference (AaDO2) is calculated. The AaDO2 is used as a measure of the degree of impairment of the lung's ability to fully oxygenate the blood. Next, as the patient wakes up from the anaesthesia, an observer (who is not involved in the clinical care of the patient) will record the amount of coughing that occurs. Assessment of coughing will involve recording: